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I had a situation where my test environment DAG was offline and not detected. I’m not sure what caused this issue, however the mailbox databases were dismounted and the Content Indexes were in a failed state. This environment has two sites with a single DAG expanding across the sites. One site is active with a single Mailbox server and one CAS/HUB multi-role server. The passive site has the same configuration.

The following was returned when I executed a Get-MailboxDatabaseCopyStatus |FL:

Attempting to mount the databases doesn’t work. I attempt to start the DAG and get the following error:

The errors associated with the Cluster API in the above figure show that the Cluster service is not in a healthy state. Furthermore, I was not able to determine which data center was the cluster owner as seen below:

After checking the cluster service in Services, I see that it’s not only disabled but greyed out as well. Therefore, I’m unable to start it. Next, I proceed to the Failover Cluster Manager snap-in and notice that none of the DAG nodes are listed. This article by Tim McMichael was helpful in resolving this issue by providing the following steps in restoring the cluster.

Since this server is running on Windows 2008 R2, I run this command: Import-Module FailoverClusters

Now I have to reset the DAG Cluster Name Object (CNO) in Active Directory. Once the object is located, you simply right click on the CNO and select reset. After this is complete the CNO has to be disabled. If it’s still enabled, you will not be able to recreate the Cluster using the existing name as Failover Cluster Manager will think it’s being used.

Finally, I’m able to recreate the Cluster in Failover Cluster Manager, I was able to restore the DAG and bring the mailbox databases back online.

In this blog, I covered the steps I used to recover from a scenario where the DAG in my Exchange 2010 test environment was offline.